Electrostatic toner

ABSTRACT

AN ELECTROSTATIC TONER COMPRISING A MULTIPLICITY OF PIGMENTED RESINOUS PARTICLES WHEREIN THE RESIN CONTAINS A POLYMERICALLY PLASTICIZED COPOLYMER OF STYRENE AND ACRYLONITRILE.

United States Patent U.S. Cl. 252-621 3 Claims ABSTRACT OF THE DISCLOSURE An electrostatic toner comprising a multiplicity of pigmented resinous particles wherein the resin contains a polymerically plasticized copolymer of styrene and acrylonitrile.

The present invention relates to electrostatic toners and, more particularly, to solid electrostatic toners.

Those skilled in the art are aware that development of electrostatic images is generally accomplished by the use of developers comprising at least in part of toners. Two types of toners are in general use commercially, liquid toners and solid toners. This invention is concerned with the latter type which, almost uniformly in practical systems, are used in association with solid carriers to form a triboelectric developer.

Solid toners comprise a multiplicity of fine particles each having an average dimension of the order of 5 to about 25 microns. The toners must have certain basic characteristics among which are capability of uniformly accepting and retaining a triboeletrically induced, electrostatic charge, capability of making the electrostatic image visible, capability of being fused or otherwise afiixed to recipient surfaces, capability of being cleaned from surfaces upon which adherence is not desirable, and capability of operating in electrostatic copying and printing machines along with carrier without excessive dusting, fire hazard and/or erosion of critical components. Economics also dictates that satisfactory toners give a relatively large number of copies per standardized quantity of toner.

While there are a number of types of solid electrostatic toners on the commercial market, each is deficient to some degree in one or more of the aforestated criteria. Some of the more annoying defects of electrostatically formed copies are in the realm of image density, edge contrast, background and half-tone reproduction. Everyone who has seen or made more than one copy on an electrostatic copier made by Xerox Corporation (referred to hereinafter as a Xerox copy), is aware that Xerox copies can, at times, be fuzzy, blurry, indistinct and have, what appears to be, fly specks in the background areas. While these difficulties are sometimes traceable to factors other than toner, very often the troublesome deficiencies in Xerox copies are due to toner deficiencies or, more subtly, in deficiencies existing in the electrostatic or triboelectric relationships between toners and cascade carriers. The deficiencies are not limited to Xerox copies but are also present in those copies made on n-type photosensitive surfaces using magnetic brush development.

The triboelectric relationship between carriers and toners comprising the developer system in electrostatic copying machines is very critical. The machine system defines the nature of the charge of the electrostatic image and, for all practical purposes, the nature of the carrier. If, as in the Xerox Corporation machines, the latent electrostatic image is positively charged, the toner must be charged negatively by rubbing against the cascade carrier beads. In the machines using Electrofax-type surfaces where the latent image usually comprises a negative charge, the toner in association with a carrier such as a magnetic brush must be charged positively. Much of the dirty back- 3,794,594 Patented Feb. 26, 1974 ground present in many electrostatic copies is due to a small portion of residual charge on the surface not eliminated by exposure to light. Lack of charge uniformity in the toner also contributes to fuzziness and loss of definition in the copies. Failure to build up an adequate charge difierential between the carrier and the toner can contribute to overall lightness in copies. While it is true that the triboelectric characteristics of a developer are equally affected by the carrier and the toner both making up the developer, as a practical matter the carrier is fixed by the parameters of the machine system being used. Thus unless one wishes to take on the task of reengineering the entire electrostatic copier system, one is forced to make whatever advances are possible in the formulation and character of the toner, leaving modifications of the carrier to the machine manufacturers.

It has now been discovered that by means of a special composition, highly advantageous toners can be produced in an economical and efiicient manner.

It is an object of the invention to provide a novel electrostatic toner.

Other objects and advantages will become apparent from the following description.

Generaly speaking, the present invention contemplates an electrostatic toner comprising about to about 97% by weight of resin containing at least about 50% by weight (based on total toner) of a polymerically plasticized copolymer of styrene and acrylonitrile and about 3% to about 20% by weight of a pigment. Advantageously, the resin employed in the toner of the present invention is a resin sold under the trade name of Piccoflex by Pennsylvania Industrial Chemical Corporation. Piccoflex resins are defined as copolymers of styrene and acrylonitrile plasticized with low molecular weight polystyrene. The remainder of the resin is advantageously a resin from the group of polystyrene and polymers and copolymers of styrene of homologues of styrene. In the toners of the present invention the acrylonitrile portion of the resin tends to act as an internal charge director and thus tends to insure uniformity of the charge sign of the toner when the toner is triboelectrically charged against a carrier. It is a function of the polymeric plasticizer to control the melting range of the resin so as to provide a melting range within the range of about C. to about C. In place of low mole weight polystyrene, other low mole weight resins such as polydivinyl benzene, polyalkyl acrylates and polyalkyl methacrylates can be used. Those skilled in the art will appreciate that various percentages of low mole weight polymeric plasticizer within the range of about 5% to about 20% by weight of total resin plus polymeric plasticizer will be effective to plasticize the resin and to induce in the resin a melting range within the range of about 85 C. to about 115 C.

The toner of the present invention is made by high shear mixing of pigment into the molten resin, cooling and chipping the thus pigmented resin and subjecting the chipped pigmented resin to air attrition grinding in a conventional air attrition mill. The final toner has an average particle size of about 10 to 15 microns.

Pigments which can be employed in the toners of the present invention usually are selected from the class of very fine particle sized carbon blacks. Considering that toner particles themselves have a major dimension of about 10 to 15 microns, it is usually necessary to employ pigments having an ultimate particle size considerably smaller than 5 microns. Channel, oil furnace and gas furnace blacks having particle diameters of about 20 to about 80 millimicrons are very suitable. As is well known to those skilled in the art, carbon black pigmented toners can contain small amounts of dyes or pigments of colors other than black to provide delicate variations in subtones. Occasionally it is desired to provide toners of colors other than black. On these occasions pigments such as titania, phthalocyanine blue, pigment reds, pigmentary azo yellows and the like can be used in place of carbon black. When organic pigments are used, it is important to select very finely divided pigments which do not bleed in the molten resin and which are stable to the degree of heat involved in toner manufacture. Within these limits almost any pigment can be used. Those skilled in the art will recognize, of course, that some pigments are easier to disperse in non-polar media than others. Accordingly, in selecting suitable pigments, ease of dispersion in molten resin is another practical criterion to be observed.

In order to give those skilled in the art a better understanding and greater appreciation of the invention, the following examples are given.

EXAMPLE I A toner is made by melting 90 parts-by-weight of Piccoflex resin containing a copolymer of styrene and acrylonitrile plasticized with low mole weight polystyrene and grinding therein while said resin is in the molten state 10 parts-by-weight of carbon black. The thus-pigmented resin is cooled and chipped. The chips are ground by air attrition in a thrust-type attritor to an average particle size of 10 to 15 microns. Toner thus produced is operable in all-existing Xerox copiermodels to produce excellent, high quality copies with substantially no undesirable background. The image density, edge contrast and half-tone reproduction in the copies. made with the toner of Example I are highly superior to the same characteristics of copies made under identical conditions with standard toner sold by Xerox Corporation. The toner of Example I can also be used with advantage to develop latent electrostatic images on zinc-oxide-coated-paper Electrofax process) using magnetic brush development.

EXAMPLE II A toner similar in composition and usage to the toner of Example I is made in the same manner as the toner of Example I except that a low mole weight polyvinyl toluene is substituted for polystyrene as the polymeric plasticizer for the styrene-acrylonitrile copolymer.

EXAMPLE III A blue toner similar in utility to the toner of Example I is made by milling about 5 parts-by-weight of copper phthalocyanine into about 95 parts-by-weight of molten Piccoflex resin, cooling said pigmented resin and grinding by air attrition to a particle size of about to about microns.

EXAMPLE IV A toner is made by melt blending 30 parts-by-weight of Foster Grant expandable polystyrene beads and 60 parts-by-weight of Piccoflex at about 123 (3., allowing the molten resin to expand and blending therein, under high shear conditions, about 10 parts-by-weight of finelydivided carbon black. The pigmented molten mass is then allowed to cool. The cooled mass is then broken up and pulverized to an average particle size of 10 to 15 microns.

4 EXAMPLE v The toner of Example IV was tested in a Xerox 3600- HI Copier made by Xerox Corporation with excellent results. A standard weight of the toner of Example IV produced 9070 copies of an original whereas an identical amount of the toner manufacture, sold and distributed by Xerox Corporation for use in this machine produced only 6830 copies of the identical original.

EXAMPLE VI The toners of Examples I to IV will attain a positive triboelectric charge by interaction with iron filings and thus are suitable for developing Electrofax negatively charged surfaces by means of the magnetic brush technique.

While the present invention has been described in conjunction with advantageous embodiments, those skilled in the art will recognize that modifications and variations may be resorted to without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the purview and scope of the invention.

1 claim:

1. A solid electrostatic toner comprising a plurality of particles, each'having an average dimension of about 10 to about 15 microns and consisting essentially of about 3% to about 20% by weight of pigment from the group consisting of carbon black, titania, phthalocyanine blue, pigment reds and pigmentary azo yellows and about to about 97% by weight of resin, said resin comprised of at least 50% by weight of a polymerically plasticized copolymer of syrene and acrylonitrile sufiiciently plasticized with low molecular weight polymer to exhibit a melting range within the range of about C. to about C. with the balance of the resin being selected from the group consisting of polymers and copolymers of styrene and homologues thereof.

2. A solid electrostatic toner as in claim 1 wherein the polymeric plasticizer is low molecular weight polystyrene in an amount of about 5% to about 20% by weight of the total resin plus polymeric plasticizer.

3. A solid electrostatic toner as in claim 1 wherein the pigment is carbon black.

References Cited UNITED STATES PATENTS 2,891,011 6/1959 Insalaco 25262.1

FOREIGN PATENTS 1,006,085 9/1965 Great'Britain 25262.1

1,042,498 9/1966 Great Britain 252-621 16,118 7/1969 Japan 252-621 1,016,072 1966 Great Britain 252-621 NORMAN G. TORCHIN, Primary Examiner J. P. BRAMMER, Assistant Examiner US. Cl. X.R. 260-41 

